Elastic wave device and duplexer

Abstract

An elastic wave device includes an unbalanced terminal and first and second balanced terminals. A longitudinally-coupled-resonator-type first elastic wave filter is provided between the unbalanced terminal and the first balanced terminal. An elastic wave filter, which is connected in parallel with the first elastic wave filter, is connected between the unbalanced terminal and the second balanced terminal. The current paths through which IDT electrodes of the elastic wave filter and the elastic wave filter are connected to ground terminals, are not symmetrical.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to elastic wave devices that utilize elastic waves, such as surface acoustic waves or boundary acoustic waves. More specifically, the present invention relates to elastic wave devices including a plurality of longitudinally-coupled-resonator-type elastic wave filters that are connected with each other.[0003]2. Description of the Related Art[0004]An RF-stage duplexer of a mobile telephone device includes a transmission-side filter and a reception-side filter. A duplexer in which a transmission-side filter and a reception-side filter are defined by elastic wave filters is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-118277.[0005]FIG. 12 is a plan view schematically illustrating the electrode structure of the duplexer described in Japanese Unexamined Patent Application Publication No. 2008-118277. A duplexer 1001 includes the illustrated electrode stru...

AI Technical Summary

Benefits of technology

[0012]To overcome the problems described above, preferred embodiments of the present invention provide an elastic wave device that is not only capable of reducing loss within the pass band, but is also capable of making the spurious level outside the pass band small and consequently is capable of improving isolation characteristics when being used together with a filter having a different pass band and to provide a duplexer that includes the elastic wave device and that has outstanding isolation characteristics.

[0021]A duplexer according to a preferred embodiment of the present invention preferably includes a reception-side filter and a transmission-side filter, the reception-side filter being defined by an elastic wave device according to a preferred embodiment of the present invention. Therefore, as compared to using a neutral-point-balance filter, not only can loss be reduced in the elastic wave filter, but also isolation of the pass band of transmission-side filter from that of the reception-side filter can be improved.

[0023]In the elastic wave device according to the first preferred embodiment, the second elastic wave filter is a float-balance-type elastic wave filter and, therefore, not only is loss reduced, but also spurious responses outside the pass band are prevented or minimized since the current path that connects an end of the first elastic wave filter to be connected to the ground potential and a ground terminal and the current path that connects an end of the second elastic wave filter that is to be connected to the ground potential and a ground terminal, are different. Consequently, the isolation characteristics are improved when the elastic wave device is used together with a filter having a different pass band.

[0024]Similarly, in the elastic wave device according to the second preferred embodiment, the second and fourth elastic wave filters are float-balance-type filters and, therefore, not only is insertion loss reduced, but also spurious responses outside the pass band are prevented or minimized since the current path that connects ends of the first and second elastic wave filters to be connected to the ground potential and a ground terminal and the current path that connects ends of the third and fourth elastic wave filters that are to be connected to the ground potential and a ground terminal, are different. Consequently, the isolation characteristics are improved when the elastic wave device is used together with a filter having a different pass band.

[0025]Therefore, when an elastic wave device according to a preferred embodiment of the present invention is used as the reception-side filter of a duplexer, isolation of the pass band of the transmission-side filter from that of the reception-side filter is effectively improved.

Problems solved by technology

However, in a float-balance-type elastic wave filter, there is a problem in that the degree of balance between signals at the first and second balanced terminals 1004 and 1005 is worse than that in a neutral-point-balance-type filter.

Consequently, in the duplexer 1001 illustrated in FIG. 12, there is a problem in that the reception-side filter 1006 is not sufficiently isolated from the pass band of the transmission-side filter 1008.

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